The "low coolant" light keeps popping on when I had already added 3 gallons of coolant. There is no obvious leaks underneath the car either. Also, the engine sounds like it is knocking pretty hard and it stalls when I pick up speed when driving it. I was adviced that the carburetor may need cleaning. I have the cleaner in hand, but I looked into the car's manual and it's not telling me where the carburetor is located. My questions are, where is the carburetor located underneath the hood and is there any other help and tips for this "low coolant" light issue?

Your 1996 Oldsmobile Cutlass Supreme does not have a carburetor, this engine uses fuel injectors. Severe dirveability concerns will generally trigger a check engine light. If the light is on, any stored fault codes should be diagnosed. As for the low coolant light. If the radiator is full and the light is on it could be that the low coolant sensor has failed. The sensor should be located in one of the radiator side tanks, near the top.

Thank you very much for the information. I will see to it that the coolant sensor is replaced. As for the engine light coming on, we had taken it to a local mechanic (twice) before for the same issue. At first he said he had fixed it. I am not sure if he had a diagnostic on the car, but the 2nd time around of taking it back to the same local mechanic, his final result was that I had threaded a spark plug wrong and said he had fixed the engine light issue. I was glad to see the check engine light was gone but then he commented "Oh the check engine light will come back. It just needs to be turned off." Til this day, the car still continues to stall and knock hard as I pick up speed. I am no longer taking my car to that particular local mechanic. As a person with a budget and average experience on doing quick fixes, is there any advice or tips for me to fix this dilemma on my own? If not, any other advice will be great.